There are many instances where the tension in a cable or wire is a critical factor in the operation and performance of a system; an example is the wire cable control system in an aircraft. Since there are typically many control cables even in a small aircraft, and since the performance of the aircraft depends on the cables having the proper tension, it is desirable to be able to obtain quick and consistently accurate tension readings of the cables for testing and adjustment purposes.
Hand-held tension testers or tensiometers are well-known in the art where a frame having first and second arms with cable-engaging portions is suspended from or clamped onto the cable being tested, and a cable-deflecting element supported by a central portion of the frame is urged against the cable to deflect it laterally between the cable-engaging portions. A spring scale mechanism connected to the cable-deflecting element registers a scale reading proportional to the force required to deflect the cable, and this reading is then typically referenced to a conversion table to determine the tension in the cable. Examples of such devices are disclosed in U.S. Pat. No. 4,135,393 to Jordan, U.S. Pat. No. 3,618,379 to Lipton, and U.S. Pat. No. 3,570,307 to Malriat and Milton.
Several disadvantages exist with such prior art tensiometers. In any given system, such as an aircraft, a variety of cable diameters are typically used. To be able to test cables of different diameters, prior art tensiometers are provided with removable, replaceable cable-deflecting elements which must be changed every time a different diameter cable is encountered. This is a time-consuming and relatively complicated procedure, and presents the problem of error in measurement due to incorrect matching of deflecting elements to a particular cable size.
Furthermore, the spring scale prior art devices described above are typically not very accurate and are very difficult to re-calibrate with any degree of accuracy. Very often the person using prior art tensiometers will have to estimate or guess at the tension in a cable based on known inaccuracies in the tensiometer. Also, frictional induced variability in the response of the mechanical spring scale mechanisms is a major limitation of the prior art.